"Say what?" you exclaim, "that doesn't make any kind of sense!"
Well here's my reasoning. My impression of google's overall strategy (outside of pushing ads at you any way they can of course) is to provide a seamless online experience, regardless of where you're logging on from. If i'm at work, or at home, or on my mobile phone, i can log onto all the various Google apps, and all the data Google has on me is shared between apps and between devices.
(As pointed out earlier, some people think this raises some serious privacy concerns. If Google ever decided to really go evil they could do so in a huge way, and even now they have at least the potential to inflict massive damage entirely by accident. But that's definitely not the issue i wanted to talk about right now.)
I really like winamp. It's a great music player. However trying to sync it between machines is a pain. I've rated... almost 4000 songs in winamp, but there is no easy way to transfer those ratings to another copy of winamp. The easiest way is to sort everything by rating in the Media Library and either add a specific tag to each rating, or to save playlists of each rating.
Which brings us to the second big problem. It can be difficult to transfer playlists between machines as well. If you keep the folder structures entirely identical then it works. Winamp is smart enough that even if all the files start with "C:\" it will check the J drive as well, for example, if that's the drive you load the playlist file from. However if the folder structure varies at all it will just choke.
So the Google music player would have something equivalent to the winamp Media Library. Except your ratings would be saved online. (Also, i'd prefer a 10 star system rather than a 5 star system, but that's a different quibble =) Every time you started the player on a new computer it would scan whatever folders you told it to and it would associate the music files it found there with the songs in your Media Library. Playlists would be stored online as well of course, with the option to save them to transfer to an offline machine of course. Actually it would be useful if you could save it in a "google" format to transfer to an offline machine with the google media player running it, or in a m3u format targeted for the file structure on a specific device, such as a mp3 player.
The tricky part would be deciding how closely a file needed to match in order to be associated with a song. The safe way to do it would be to require an exact match (file size and hash key matching presumably) but then provide a menu to merge files into a song if you thought they were close enough. Definitely if there's any kind of automatic merging there would need to be an option to undo it. "I don't care that it's the same song, it's two different recordings and i want two different listings!"
I suppose there should be possible the Google music player to handle the file structure itself in case you're one of the people who likes how iTunes handles things, but there ought to be an option (oohhh! evil!) to handle generic file trees so you can structure it however you wish.
Given my usual naming conventions, the Google Music Player clearly ought to be named "Goompa." I'd say it should have a little mushroom mascot as well, but that would probably get them in trouble :)
Oh yeah, and in addition to just another way to keep people as a captive audience and server up ads, i'm sure Google would find great ways to mine the information about what music you liked, how often you listened to it, etc. And with the new Buzzy focus on Facebooky stuff i'm sure they'd eventually add tools to do things like find out what the highest rated songs of all your friends are and such.
The big downside of course would be that if it took off it would probably make Google the #1 target for RIAA subpoenas =P
Of course after my experience with Chrome i'd be worried that if Google did make a music player they'd make the UI ugly and drop half the features other players have come up with because the designers didn't think they were good enough ;)
(And i'm sure that now a certain someone will tell me that i ought to get a job at Google and make this my pet project ;)